Optical switching in lidar systems

ABSTRACT

A LIDAR system is configured to generate an outgoing light signal that exits from the LIDAR system. The LIDAR system is configured to receive an incoming light signal that enters the LIDAR system and that includes light from the outgoing light signal. The LIDAR system also includes an optical switch that receives the outgoing light signal and the incoming light signal and is configured to be operated in different modes. The incoming light signal and/or the outgoing light signal are routed along different optical paths through the LIDAR system in response to the optical switch being in different modes.

RELATED APPLICATIONS

This Patent Application is related to U.S. Provisional PatentApplication Ser. No. 62/745,225, filed on Oct. 12, 2018, and entitled“Optical Sensor System,” and to U.S. Provisional Patent Application Ser.No. 62/784,111, filed on Dec. 21, 2018, entitled “Optical SensorSystem,” each of which is incorporated herein in its entirety. Thisapplication is related to PCT Application No. PCT/US19/54160, filed Oct.1, 2019.

FIELD

The invention relates to optical devices. In particular, the inventionrelates to LIDAR systems.

BACKGROUND

LIDAR technologies are being applied to a variety of applications. OneLIDAR technique makes use of a LIDAR system that generates an outgoinglight signal. The LIDAR system also outputs from the system a LIDARoutput signal that includes a portion of the light from the outgoinglight signal. The LIDAR output signal is reflected off of an object andat least a portion of the reflected light returns to the LIDAR system asa LIDAR input signal. The LIDAR system combines the LIDAR input signalwith a reference signal so as to generate a composite signal. Thereference signal includes a second portion of the light from theoutgoing light signal that did not exit from the LIDAR system and wasnot reflected by the object. The LIDAR system uses the composite signalto generate LIDAR data for the object (distance and/or radial velocitybetween the source of a LIDAR output signal and a reflecting object).

It is often desirable for the LIDAR input signal to be received throughthe same facet through which the LIDAR output signal is transmitted(sometimes called a coaxial configuration). Accordingly, a portion ofthe path traveled by the LIDAR input signal and the LIDAR output signalthrough the LIDAR system can be the same (common optical path); however,the LIDAR system can separate the path of the LIDAR input signal fromthe path of the LIDAR output signal in order to combine the LIDAR inputsignal with the reference signal. The signals are often separated bytechnologies such as couplers and circulators.

It is desirable to build these LIDAR systems on optical chips usingplatforms such as the silicon-on-insulator platform. However,circulators are not practical for integration onto these optical chips.Additionally, since optical couplers spilt a signal, optical couplersare a source of power loss for the LIDAR input signal. As a result,there is a need for a LIDAR system that can separate a LIDAR inputsignal and the LIDAR output signal that travel on the same optical path.

SUMMARY

A LIDAR system is configured to generate an outgoing light signal thatexits from the LIDAR system. The LIDAR system is configured to receivean incoming light signal that enters the LIDAR system and that includeslight from the outgoing light signal. The LIDAR system also includes anoptical switch that receives the outgoing light signal and the incominglight signal and is configured to be operated in different modes. Theincoming light signal and/or the outgoing light signal are routed alongdifferent optical paths through the LIDAR system in response to theoptical switch being in different modes.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic of a LIDAR system.

FIG. 2A illustrates an example of a frequency versus time schedule foran outgoing light signal and an incoming light signal at an exit from aLIDAR system.

FIG. 2B illustrates another example of a frequency versus time schedulefor an outgoing light signal and an incoming light signal at an exitfrom a LIDAR system.

FIG. 2C illustrates another example of a frequency versus time schedulefor an outgoing light signal and an incoming light signal at an exitfrom a LIDAR system.

FIG. 2D illustrates a separation threshold (ST) as a function of areceive ratio.

FIG. 3 illustrates multiple light sources configured to generate anoutgoing light signal that includes multiple channels.

FIG. 4 illustrates a light source that includes multiple laser sources.

FIG. 5 illustrates one example of a structure configured to generate alight signal that includes multiple channels.

FIG. 6A illustrates an example of a processing unit.

FIG. 6B provides a schematic of electronics that are suitable for usewith a processing unit constructed according to FIG. 6A.

FIG. 6C provides another schematic of electronics that are suitable foruse with a processing unit constructed according to FIG. 6A.

FIG. 7 illustrates an example of an optical port that includes beamsteering capability.

FIG. 8 illustrate construction of an optical switch that is suitable foruse in planar optical devices.

DESCRIPTION

The LIDAR system generates an outgoing light signal and outputs a LIDARoutput signal that includes a first portion of the light from theoutgoing light signal. The LIDAR output signal is reflected off of anobject and at least a portion of the reflected light returns to theLIDAR system as a LIDAR input signal. The LIDAR system combines theLIDAR input signal with a reference signal so as to generate a compositesignal. The reference signal includes a portion of the light from theoutgoing light signal that did not exit from the LIDAR system and wasnot reflected by the object. The LIDAR system uses the composite signalto generate LIDAR data for the object (distance and/or radial velocitybetween the source of a LIDAR output signal and a reflecting object).

The LIDAR input signal and the LIDAR output signal travel along the samepath between a signal-directing component and a facet of a waveguide.The signal-directing component is an optical switch that is operated soas to separate the pathway of the LIDAR input signal from the pathway ofthe LIDAR output signal. Optical switches can be integrated into opticalchip platforms such as the silicon-on-insulator platform. Additionally,the switch does not significantly reduce the power of the LIDAR inputsignal. As an additional and unexpected advantage, the optical switchcan greatly reduce the amount of laser energy that exits from the LIDARsystem and enters the environment. As a result, the optical switchprovides a LIDAR system that can provide protection for the environmentand the eyes of users and bystanders.

FIG. 1 is a schematic of a LIDAR system. The system includes a lightsource 10 such as a laser that outputs an outgoing light signal. Theoutgoing light signal includes one or more different channels that areeach at a different wavelength. When the outgoing light signal includesmultiple channels, the wavelengths of the channels can be periodicallyspaced in that the wavelength increase from one channel to the nextchannel is constant or substantially constant. A suitable light source10 for generating an outgoing light signal with a single channelincludes semiconductor lasers, solid-state lasers, gas lasers, andliquid lasers. A suitable light source 10 for generating multiplechannels with periodically spaced wavelengths includes, but is notlimited to, comb lasers, multiple single wavelength lasers multiplexedinto to single optical waveguide, and sources such as that described inU.S. patent application Ser. No. 11/998,846, filed on Nov. 30, 2017,grated patent number U.S. Pat. No. 7,542,641, entitled “Multi-ChannelOptical Device,” and incorporated herein in its entirety.

The LIDAR system also includes a utility waveguide 12 that receives theoutgoing light signal from the light source 10. A modulator 14 isoptionally positioned along the utility waveguide 12. The modulator 14is configured to modulate the power of the outgoing light signal andaccordingly the LIDAR output signal(s). The electronics can operate themodulator 14. Accordingly, the electronics can modulate the power of theoutgoing light signal and accordingly the LIDAR output signal(s).Suitable modulators 14 include, but are not limited to, PIN diodecarrier injection devices, Mach-Zehnder modulator devices, andelectro-absorption modulator devices. When the modulator 14 isconstructed on a silicon-on-insulator platform, a suitable modulator isdisclosed in U.S. Patent application Ser. No. 617,810, filed on Sep. 211993, entitled Integrated Silicon PIN Diode Electro-Optic Waveguide, andincorporated herein in its entirety.

An amplifier 16 is optionally positioned along the utility waveguide 12.Since the power of the outgoing light signal is distributed amongmultiple channels, the amplifier 16 may be desirable to provide each ofthe channels with the desired power level on the utility waveguide 12.Suitable amplifiers include, but are not limited to, semiconductoroptical amplifiers (SOAs).

The utility waveguide 12 carries the outgoing light signal from themodulator 14 to a signal-directing component 18. The signal-directingcomponent 18 can direct the outgoing light signal to a LIDAR branch 20and/or a data branch 22. The LIDAR branch outputs LIDAR output signalsand receives LIDAR input signals. The data branch processes the LDARinput signals for the generation of LIDAR data (distance and/or radialvelocity between the source of the LIDAR output signal and a reflectingobject).

The LIDAR branch includes a LIDAR signal waveguide 24 that receives atleast a portion of the outgoing light signal from the signal-directingcomponent 18. The LIDAR signal waveguide 24 carries at least a portionof the outgoing light signal to an optical port 26 through which lightsignals enter and/or exit from the LIDAR system. In some instances, theoptical port 26 is a facet positioned at an edge of an LIDAR chip. Whenthe outgoing light signal includes multiple different channels atdifferent wavelengths, the optical port 26 can have demulitplexerfunctionality and/or can include or consist of a demulitplexer thatseparates the outgoing light signal into multiple LIDAR output signalsthat are each at a different wavelength (channel) and are directed todifferent sample regions in a field of view. The optical port 26 outputsthe LIDAR output signals which can be reflected by a reflecting object(not shown) located outside of the LIDAR system. The reflected LIDARoutput signals return to the optical port 26 as LIDAR input signals. Theoptical port 26 combines the LIDAR input signals and outputs the resulton the LIDAR signal waveguide 24 as an incoming light signal.

In some instances, the optical port 26 includes beam steeringfunctionality. In these instances, the optical port 26 can be inelectrical communication with electronics (not shown) that can operatethe optical port 26 so as to steer the LIDAR output signals to differentsample regions in a field of view. The optical port 26 and/orelectronics can be configured such that the different LIDAR outputsignals are steered independently or are steered concurrently.

Although the optical port 26 is illustrated as a single component, theoptical port 26 can include multiple optical components and/orelectrical components. Suitable optical ports include, but are notlimited to, optical phased arrays (OPAs), transmission diffractiongratings, reflection diffraction gratings, and Diffractive OpticalElements (DOE). Suitable optical port 26 with beam steering capabilityinclude, but are not limited to, optical phased arrays (OPAs) withactive phase control elements on the array waveguides.

The LIDAR signal waveguide 24 carries the incoming light signal to thesignal-directing component 18. Since the outgoing light signal alsotravels between the optical port 26 and the signal-directing component18 on the LIDAR signal waveguide 24, the incoming light signal and theoutgoing light signal travel a common optical path between the opticalport 26 and the signal-directing component 18. The outgoing light signaltravels away from the signal-directing component 18 along the commonoptical pathway and the incoming light signal travels toward thesignal-directing component 18 along the common optical pathway. Thesignal-directing component 18 directs the incoming light signal to theutility waveguide 12 and/or a comparative signal waveguide 28. Theportion of the incoming light signal-directed to the comparative signalwaveguide 28 serves as a comparative incoming light signal.

The comparative signal waveguide 28 carries the comparative incominglight signal to a comparative demultiplexer 30. When the comparativelight signal includes multiple channels, the comparative demultiplexer30 divides the comparative incoming light signal into differentcomparative signals that each has a different wavelength. Thecomparative demultiplexer 30 outputs the comparative signals ondifferent comparative waveguides 32. The comparative waveguides 32 eachcarry one of the comparative signals to different processing components34.

The signal-directing component 18 is configured such that when thesignal-directing component 18 directs at least a portion of the incominglight signal to the comparative waveguide 32, the signal-directingcomponent 18 also directs at least a portion of the outgoing lightsignal to a reference signal waveguide 36. The portion of the outgoinglight signal received by the reference signal waveguide 36 serves as areference light signal.

The reference signal waveguide 36 carries the reference light signal toa reference demultiplexer 38. When the reference light signal includesmultiple channels, the reference demultiplexer 38 divides the referencelight signal into different reference signals that each has a differentwavelength. The reference demultiplexer 38 outputs the reference signalson different reference waveguides 40. The reference waveguides 40 eachcarry one of the reference signals to a different one of the processingcomponents 34.

The comparative waveguides 32 and the reference waveguides 40 areconfigured such that a comparative signal and the correspondingreference signal are received at the same processing component 34. Forinstance, the comparative waveguides 32 and the reference waveguides 40are configured such that the comparative signal and the correspondingreference signal of the same wavelength are received at the sameprocessing component 34.

As will be described in more detail below, the processing components 34each combines a comparative signal with the corresponding referencesignal to form a composite signal that carries LIDAR data for a sampleregion on the field of view. Accordingly, the composite signal can beprocessed so as to extract LIDAR data for the sample region. Thesignal-directing component 18 can be an optical switch such as across-over switch. A suitable cross-over switch can be operated in aswitched mode or a pass mode. In the pass mode, the outgoing lightsignal is directed to the LIDAR signal waveguide 24 and an incominglight signal would be directed to the utility waveguide 12. In theswitched mode, the outgoing light signal is directed to the referencesignal waveguide 36 and the incoming light signal is directed to thecomparative signal waveguide 28. Accordingly, the incoming light signalor a portion of the incoming light signal can serve as the comparativelight signal and the outgoing light signal or a portion of the outgoinglight signal can serve as the reference light signal.

The different modes of switch operation described above are configuredsuch that the outgoing light signal exits from the LIDAR system when theoptical switch is in the pass mode (first mode) but does not exit fromthe LIDAR system when the optical switch is in the switched mode (secondmode). The incoming light signal and the outgoing light signal bothtravel along the common optical path when the optical switch is in thepass mode. The incoming light signal travels along the common opticalpath when the optical switch is in the switched mode but the outgoinglight signal does not travel along the common optical path when theoptical switch is in the pass mode. The incoming light signal travelsaway from the optical switch along a first optical path that includesall or a portion of the comparative signal waveguide 28 when the opticalswitch is in the pass mode and the outgoing light signal travels awayfrom the optical switch along a second optical path that includes all ora portion of the reference signal waveguide 36 when the optical switchis in the switched mode. The first optical path, the second optical pathand the common optical path are separate from one another. Light fromthe outgoing light signal is mixed with light from the incoming lightsignal so as to generate the composite light signal when the opticalswitch is in the switched mode. The composite light signal is notgenerated when the optical switch is in the first mode.

An optical switch such as a cross-over switch can be controlled by theelectronics. For instance, the electronics can control operate theswitch such that the switch is in the switched mode or a pass mode. Whenthe LIDAR output signal is to be transmitted from the LIDAR system, theelectronics operate the switch such that the switch is in the pass mode.When the LIDAR input signal is to be received by the LIDAR system, theelectronics operate the switch such that the switch is in the switchedmode. The use of a switch can provide lower levels of optical loss thanare associated with the use of an optical coupler as thesignal-directing component 18.

In the above descriptions of the operation of the signal-directingcomponent 18, the comparative light signals and the reference lightsignals are concurrently directed to the data branch. As a result, theprocessing components 34 can each combine a comparative signal with thecorresponding reference signal.

In some instances, an optical amplifier 42 is optionally positionedalong the LIDAR signal waveguide 24 and is configured to provideamplification of the outgoing light signal and/or of the incoming lightsignal. Accordingly, the effects of optical loss at the signal-directingcomponent 18 can be reduced.

During operation of the LIDAR system, the generation of LIDAR data isdivided into a series of cycles where LIDAR data is generated for eachcycle. In some instances, each of the cycles corresponds to a differentsample region in a field of view. Accordingly, different cycles cangenerate LIDAR data for different regions in a field of view.

The cycles can be performed such that the time for each cycle can bedivided into different time periods. The electronics can add chirp tothe frequency of the outgoing light signal and accordingly to the LIDARoutput signal(s). The chirp can be different during adjacent periods ina cycle. For instance, the electronics can increase the frequency of theoutgoing light signal during a first period and decrease the frequencyof the outgoing light signal during a second period.

The following FIG. 2A through FIG. 2D illustrate the results ofoperating a LIDAR system using the optical switch disclosed. In order tosimplify the illustration, FIG. 2A through FIG. 2D are directed to asingle channel in an outgoing light signal or treat the LIDAR system asgenerating an outgoing light signal with a single channel.

FIG. 2A illustrates an example of a possible frequency versus timeschedule for the frequency of the outgoing light signal at the facet andthe incoming light signal at the facet. The schedule is shown forseveral different cycles labeled cycle, through cycle_(i+2). As notedabove, different cycles can correspond to different sample regions in afield of view. As a result, the LIDAR system can steer the LIDAR outputsignal(s) from one sample region in the field of view to another sampleregion in the field of view between different cycles.

Each cycle includes a first period labeled “Period,” and a second periodlabeled “Period₂.” The illustrated chirp is different for differentperiods in a cycle. Accordingly, the outgoing light signal is adifferent function of time than the incoming light signal. For instance,the frequency of the outgoing light signal increases during the firstperiod and decreases during the second period. Although each of thecycles is shown in FIG. 2A as having two periods, the cycles can includeone, two, or more than two periods.

Each period includes multiple time segments. The electronics can operatethe signal-directing component 18 in different modes during differenttime segments. For instance, in FIG. 2A, each period includes a transmitsegment and a receive segment. During the transmit segment, theelectronics can operate a signal-directing component 18 such as anoptical switch in the pass mode where the outgoing light signal isdirected to the LIDAR signal waveguide 24 as illustrated by the solidline labeled “outgoing light signal” in FIG. 2A. As a result, one ormore LIDAR output signals are output from the LIDAR system during thetransmit segment.

During the receive segment, the electronics can operate asignal-directing component 18 such as an optical switch in the switchedmode where the outgoing light signal is directed to the reference signalwaveguide 36 so the outgoing light signal or a portion of the outgoinglight signal can serve as the reference light signal. As a result, theoutgoing light signal is not received at the facet during the receivesegment. In order to illustrate this result, the portion of the LIDARoutput signal in the receive segment is shown as a dashed line in FIG.2A. Accordingly, during the receive segment, the “outgoing light signal”continues to be generated by the LIDAR system but is not output as theone or more LIDAR output signals. Since the one or more LIDAR outputsignals are not output from the LIDAR system during the receive segment,the amount of laser energy introduced into the atmosphere is reduced andthe possibility of eye damage from the LIDAR system is reduced.Additionally, during the receive segment, the incoming light signal isdirected to the comparative signal waveguide 28 allowing the incominglight signal or a portion of the incoming light signal to serve as thecomparative light signal.

During subsequent transmit segments, previously transmitted LIDAR outputsignal may continue returning to the LIDAR system as LIDAR inputsignals. The resulting incoming light signal can still be received onthe LIDAR signal waveguide 24, however, since the electronics operatethe signal-directing component 18 in the pass mode during the transmitsegments, the received incoming light signal are not passed to a databranch 22. For instance, in the LIDAR system of FIG. 1, the incominglight signal is directed to the utility waveguide 12 where it generallydoes not have enough power to affect operation of the light source(s).In instances, where it is desirable to reduce the intensity of theincoming light signal on the utility waveguide 12, it is possible toreduce the power of the outgoing light signal through one or moremechanisms selected from the group consisting of reducing amplificationprovided by an amplifier 16, tuning the output from the light source andoperating an optical attenuator (not shown) on the utility waveguide 12.Since the incoming light signal is directed to the utility waveguide 12during the transmit segments, the electronics do not generate LIDAR datafrom incoming light signals received during the transmit segments. Thisresult is illustrated by the portion of the incoming light signals shownby dashed lines during the transmit segments of FIG. 2A.

In a LIDAR system, the roundtrip signal time τ represents the time for aLIDAR output signal to travel to a reflecting object and to return tothe LIDAR system. As a result, the roundtrip signal time (τ) can berepresented by τ=2D/c where D represents the displacement distancebetween the reflecting object and the location where the LIDAR outputsignal exits from the LIDAR system. LIDAR systems are generallyassociated with a maximum distance (D_(max)). The maximum distance isthe largest separation between an object and the LIDAR system for whichthe LIDAR system generates LIDAR data. FIG. 2A is generated using theassumption that the displacement distance (D) is equal to the maximumdisplacement distance (D_(max)). When the displacement distance (D) isequal to the maximum displacement distance (D_(max)), the time between aLIDAR output signal exiting the LIDAR system and returning to the LIDARsystem can be represented by τ_(max) (τ_(max)=2D_(max)/c where c is thespeed of light). FIG. 2A represents the situation where τ=τ_(max). As aresult, the duration of the transmit segment is equal to the time neededfor a LIDAR output signal to travel from the LIDAR system to an objectlocated at the maximum distance and then back to the LIDAR system. As aresult, the LIDAR system begins to receive the incoming light at the endof the transmit segment. Accordingly, the line labeled “incoming lightsignal” in FIG. 2A represents the receipt of the “incoming light signal”at the start of each receive segment.

FIG. 2B illustrates the frequency versus time schedule of FIG. 2Amodified to show the results when the reflecting object is locatedcloser to the LIDAR system than in FIG. 2A. In particular FIG. 2Brepresents the situation where τ=the duration of the receive segment(T_(rs)). Accordingly, in period 1 of cycle i, the incoming light signalresulting from a LIDAR output signal transmitted in cycle 1 first showsup in the transmit segment after passage of an amount of time equal tothe duration of the receive segment as shown by the time labeled t_(rs).

The electronics use data generated from the incoming light signal duringthe receive segment to generate the LIDAR data. The reliability of theLIDAR data increases the longer that the incoming light signal isavailable to the electronics. As is evident in FIG. 2A and FIG. 2B, theincoming light signal is available to the electronics for generating theLIDAR data during the entire duration of the receive segment.

As the distance between the LIDAR system and the object becomes closeenough that the roundtrip signal time (τ) becomes less than duration ofthe receive segment (T_(rs)), the incoming light signal becomesavailable to the electronics for generating the LIDAR data for afraction of the duration of the receive segment (i.e. <100% T_(rs)). Forinstance, FIG. 2C illustrates the frequency versus time schedule of FIG.2A modified to show the results when the reflecting object is locatedcloser to the LIDAR system than in FIG. 2A. In particular FIG. 2Crepresents the situation where τ<T_(rs). Accordingly, in period 1 ofcycle i, the incoming light signal resulting from a LIDAR output signaltransmitted in cycle 1 first shows up in the transmit segment beforepassage of the amount of time equal to the duration of the receivesegment (t_(rs)).

During the transmit segments in FIG. 2C, the close proximity of theLIDAR system and the reflecting object causes the incoming light signalto return to the LIDAR system quickly. Additionally, the frequency ofthe outgoing light signals that exit from the LIDAR system does notexceed an upper frequency labeled f_(max) in FIG. 2C because f_(max)corresponds to the frequency where the electronics change thesignal-directing component 18 from the pass mode to the switched mode.As a result, the highest frequency of the incoming light signalcorresponds to incoming light signal generated from the outgoing lightsignal with a frequency of f_(max). The quick return of the incominglight signal combined with the frequency cut-off at f_(max) reduces theavailability of the incoming light signal to the electronics during thereceive segment. For instance, the portion of the incoming light signalillustrated at the solid line in FIG. 2C illustrates the portion of theincoming light signal that is available to the electronics. As shown inFIG. 2C, the incoming light signal is only available to the electronicsa portion of the entire duration of the receive segment. The LIDAR databecomes less reliable as the percentage of the receive segment for whichthe incoming light signal is available decreases. Accordingly, theincoming light signal becomes available to the electronics for less than100% of the receive segment in response to the LIDAR system and thereflecting object becoming closer than a separation threshold, but theincoming light signal is available to the electronics for 100% of thereceive segment in response to the LIDAR system and the reflectingobject becoming closer than a separation threshold.

FIG. 2D illustrates the separation threshold (ST) as a function of thereceive segment duration where the receive segment duration is shown asthe percentage of the period (100*t_(rs)/t_(p)). In FIG. 2D, the y-axisrepresents the radial distance between the LIDAR system and thereflecting object (R) and is expressed as a percentage of the maximumdistance (100*R/D_(max)). The curve labeled ST represents the separationthreshold and can be expressed as 100*A/(1−A) where A represents thereceive ratio (t_(rs)/t_(p)). Accordingly, for radial distances at orabove the separation threshold (ST), the incoming light signal isavailable to the electronics for 100% of the receive segment and forradial distances below the separation threshold (ST), the incoming lightsignal is available to the electronics for less than 100% of the receivesegment.

As is evident from FIG. 2D, the incoming light signal is not availableto the electronics for 100% of the receive segment when the receivesegment is more than 50% of the period. Accordingly, the duration of thereceive segment (t_(rs)) is selected to be less than or equal to 50% ofthe period (t_(p)). Suitable receive ratios (the percentage of a periodthat is the receive segment, t_(rs)/t_(p)) include, but are not limitedto, receive ratios greater than 10%, 20%, or 30% and/or less than 40%,45%, or 50%.

The electronics can tune the value of the transmit segment duration(t_(ts)) and/or the receive segment duration (t_(rs)) so as to increasethe reliability of the LIDAR data. For instance, the electronics cantune the value of the transmit segment duration (t_(ts)) and/or thereceive segment duration (t_(rs)) such that the LIDAR signal isavailable to the electronics for more than 90% or 100% of the receivesegment when the receive segment is more than 50% of the period. Forinstance, the electronics can tune the value of the transmit segmentduration (t_(ts)) such that the roundtrip signal time (τ) is greaterthan or equal to the duration of the receive segment (t_(rs)). Forinstance, when the displacement distance (D) decreases, the roundtripsignal time (τ=2D/c) also decreases. In response to the roundtrip signaltime (τ) being or becoming less than the duration of the receive segment(t_(rs)), the electronics can reduce the value of the duration of thereceive segment (t_(rs)) to a value that is less than or equal to theroundtrip signal time (τ). In some instances, the duration of thereceive segment (t_(rs)) can be decreased to levels that are undesirablyshort for proper generation of the LIDAR data. As a result, theelectronics can also adjust the duration of the receive segment (t_(rs))upwards. For instance, in response to the roundtrip signal time (τ)being or becoming greater than the duration of the receive segment(t_(rs))*adjustment factor₁, the electronics can increase the value ofthe duration of the receive segment (t_(rs)) to a value that is greaterthan or equal to the duration of the receive segment (t_(rs))*adjustmentfactor₂. Suitable values for adjustment factor₁ include values greaterthan or equal to 1, 1.2, or 1.4 and/or less than 1.6, 1.8, or 2.Suitable values for adjustment factor₂ include values greater than orequal to 1, 1.2, or 1.4 and/or less than 1.6, 1.8, or 2. Adjustmentfactor₁ can be the same or different from adjustment factor₂. In theabove examples, the value of the duration of the receive segment istuned. Accordingly, the receive ratio is tuned in response to changes inthe displacement distance. In the above examples, for a givendisplacement distance, the receive ratios are effectively tuned toprovide a result located at or above the curve labeled ST in FIG. 2D.For instance, the value of t_(rs) is tuned to provide a receive ratio(t_(rs)/t_(p)) that is below the value of the receive ratio provided byD′/(1+D′) where D′=D/D_(max). In one example, the value of t_(rs) istuned in response to changes in the value of D. In another example, thevalue of t_(rs) is tuned in response to the receive ratio (t_(rs)/t_(p))increasing to a value above D′/(1+D′). In another example, the value oft_(rs) is tuned in response to changes in the value of D where thereceive ratio (t_(rs)/t_(p)) increases to a value above D′/(1+D′) but isnot tuned when the change to the value of D results in a receive ratio(t_(rs)/t_(p)) remains below D′/(1+D′).

The above discussion discloses the displacement distance (D and D_(max))as representing a distance between a reflecting object and an exitthrough which the outgoing light signal exits from the LIDAR system.However, in many LIDAR applications, the distance of the reflectingobject changes during operation of the LIDAR system. As a result, inaddition or as an alternative to representing the distance between thereflecting object and the exit, the displacement distance (D andD_(max)) can represent the distance of the field of view from the exitthrough which the outgoing light signal exits from the LIDAR system.

As noted above, the roundtrip time (τ) is a function of the displacementdistance (τ=2D/c). Accordingly, electronics that know the roundtrip timeare also effectively aware of displacement distance (D). The electronicscan use a variety of different mechanisms for identifying thedisplacement distance that is to be used in tuning the transmit segmentduration (t_(ts)) and/or the receive segment duration (t_(rs)). Forinstance, a device that includes the LIDATR system can have differentmode setting that are each associated with a different displacementdistance. As an example, a device such as a phone or camera can have afacial recognition mode and a room-scan mode. When the device is infacial recognition mode, the electronics can use a first displacementdistance associated with the facial recognition mode. When the device isin room-scan mode, the electronics can use a second displacementdistance associated with the room-scan mode. Additionally oralternately, an operator can enter the displacement distance into thedevice using a user interface. Additionally or alternately, the devicecan include an auto-focus mechanism that measures displacement distance.The auto-focus can be included in the electronics or can be part of analternate application in the device. For instance, the auto-focus can bethe auto-focus of a camera included in device. The displacement distancedetermined from the auto-focus can be provided to the electronics fromthe alternate application. The electronics can use the provideddisplacement distance as the displacement distance for the field of viewin the LIDAR application or can perform additional processing of theprovided displacement distance to determine the field that is used asthe displacement distance for the field of view in the LIDARapplication. As an example, the electronics can use the result ofmultiplying the provided displacement distance by a factor to generatethe displacement distance of the field of view in the LIDAR application.

Although the above LIDAR systems are illustrated as having a singlelight source 10, the LIDAR system can have multiple light sources 10 asillustrated in FIG. 3. The light source 10 includes M light sources 10that each generates N channels. The channels are each received on achannel waveguide 80. The channel waveguides carry the channels to achannel multiplexer 82 that combines the channels so as to form theoutgoing light signal that is received on the utility waveguide 12.

In FIG. 3, each of the channels is labeled λ_(i,j) where i is the numberof the light source 10 and is from 1 to M and j is the number of thechannel for light source 10 j and is from 1 to N. As noted above, thelight sources 10 can be configured such that the wavelengths of thechannels are periodically spaced in that the wavelength increase fromone channel to the next channel (Δλ) is constant or substantiallyconstant. In some instances, the light sources 10 are configured suchthat channels with adjacent wavelengths are generated by different lightsources 10. For instance, the light sources 10 can be configured suchthat λ_(i,j)=λ_(o)+((i−1)+(j−1)(M))(Δλ). Suitable light sources 10 forthis configuration include, but are not limited to, comb lasers. In thisconfiguration, the channel multiplexer can be a cyclic multiplexerdesigned with the wavelength spacing ((N−1)*Δλ) equal to a multiple ofthe Free Spectral Range (FSR) of the channel multiplexer. Accordingly,the channel multiplexer can be designed to cycle over the wavelengthrange ((N−1)*Δλ). A suitable cyclic multiplexer includes, but is notlimited to, the ‘colorless’ AWG from Gemfire (8-Channel Cyclic ArrayedWaveguide Grating, 2018).

Suitable values for the number of light sources 10 (M) include, but arenot limited to, values greater than or equal to 2, 4, or 8, and/or lessthan 16, 32, or 64. Suitable values for the number of channels providedby a light sources 10 (N) include, but are not limited to, valuesgreater than or equal to 2, 4, or 8, and/or less than 16, 32, or 64.Suitable values for the wavelength increase from one channel to the nextchannel (Δλ) include, but are not limited to, values greater than orequal to 0.2 nm, 0.4 nm, or 0.6 nm, and/or less than 0.8 nm, 1.0 nm, or1.5 nm. Suitable values for the wavelength of the channel with theshortest wavelength include, but are not limited to, values greater thanor equal to 1.3 μm, 1.4 μm, or 1.5 μm, and/or less than 1.6 μm, 1.7 μm,or 1.8 μm. In one example, the LIDAR system includes M greater than orequal to 2, 4, or 8, and/or less than 16, 32, or 64; N greater than orequal to 2, 4, or 8, and/or less than 16, 32, or 64; and Δλ greater thanor equal to 0.2 nm, 0.4 nm, or 0.6 nm, and/or less than 0.8 nm, 1 nm, or1.5 nm.

In some instances, the light sources 10 are configured such that atleast a portion of the light sources 10 each generates two or morechannels with adjacent wavelengths. For instance, the light sources 10can be configured such that λ_(i,j)=λ_(o)+((j−1)+(i−1)(N))(Δλ). Suitablelight sources 10 for this configuration include, but are not limited to,comb lasers. In this configuration, the channel multiplexer can be abroadband multiplexer with a bandwidth of at least NΔλ. Suitablebroadband multiplexers include, but are not limited to, arrayedwaveguide gratings (AWG) and thin film filters.

As noted above, one or more of the light sources 10 can be a comb laser.However, other constructions of the light source 10 are possible. Forinstance, FIG. 4 illustrates an example of a light source 10 thatincludes multiple laser sources 84. The light source 10 illustrated inFIG. 4 includes multiple laser sources 84 that each outputs one of thechannels on a source waveguide 86. The source waveguides 86 carry thechannels to a laser multiplexer 88 that combines the channels so as toform a light signal that is received on a channel waveguide or theutility waveguide 12. The electronics can operate the laser sources 84so the laser sources 84 concurrently output each of the channels.Suitable lasers for use with a light source 10 constructed according toFIG. 4 include, but are not limited to, external cavity lasers,distributed feedback lasers (DFBs), and Fabry-Perot (FP) lasers.External cavities lasers are advantageous in this embodiment because oftheir generally narrower linewidths, which can reduce noise in thedetected signal.

FIG. 5 illustrates another example of a possible light source 10construction. The light source 10 includes a gain element 90 such as thegain element of a semiconductor laser. A gain waveguide 92 is opticallyaligned with the gain element so as to receive a light signal from thegain element. In some instances, the gain waveguide excludes the gainmedium included in the gain element. For instance, the gain waveguidecan be a ridge waveguide on a silicon-on-insulator chip. Multiplepartial return devices 94 are positioned along the gain waveguide suchthat the partial return devices interact with the light signal.

During operation, electronics operate the gain element such that thegain medium outputs the light signal. The partial return devices 94 eachpasses a portion of the light signal. The portion of the light signalthat the utility waveguide 12 receives from the partial return devicesserves as the outgoing light signal. The partial return devices alsoreturn a portion of the light signal to the gain element such that thereturned portion of the light signal travels through the gain element.The gain element can include a fully or partially reflective layer thatreceives returned portion of the light signal from the gain element andreflects the returned portion of the light signal back to the gainelement allowing the returned portion of the light signal to amplify andlase. Accordingly, the light source 10 can be an external cavity laser.

The partial return devices can be configured such that the each partialreturn device returns a different wavelength of light. For instance, thepartial return devices can be configured such that the wavelength ofeach one of the channels that is to be output by the light source 10 isreturned by at least one of the partial return devices. As a result,each of the desired channels will lase and be present in the outgoinglight signal. Suitable partial return devices include, but are notlimited to, Bragg gratings.

FIG. 6A through FIG. 6B illustrate an example of a suitable processingcomponents for use in the above LIDAR systems. A first splitter 102divides a reference signal carried on a reference waveguide 40, 52, or58 onto a first reference waveguide 110 and a second reference waveguide108. The first reference waveguide 110 carries a first portion of thereference signal to a light-combining component 111. The secondreference waveguide 108 carries a second portion of the reference signalto a second light-combining component 112.

A second splitter 100 divides the comparative signal carried on thecomparative waveguide 30, 72, or 74 onto a first comparative waveguide104 and a second comparative waveguide 106. The first comparativewaveguide 104 carries a first portion of the comparative signal to thelight-combining component 111. The second comparative waveguide 108carries a second portion of the comparative signal to the secondlight-combining component 112.

The second light-combining component 112 combines the second portion ofthe comparative signal and the second portion of the reference signalinto a second composite signal. Due to the difference in frequenciesbetween the second portion of the comparative signal and the secondportion of the reference signal, the second composite signal is beatingbetween the second portion of the comparative signal and the secondportion of the reference signal. The light-combining component 112 alsosplits the resulting second composite signal onto a first auxiliarydetector waveguide 114 and a second auxiliary detector waveguide 116.

The first auxiliary detector waveguide 114 carries a first portion ofthe second composite signal to a first auxiliary light sensor 118 thatconverts the first portion of the second composite signal to a firstauxiliary electrical signal. The second auxiliary detector waveguide 116carries a second portion of the second composite signal to a secondauxiliary light sensor 120 that converts the second portion of thesecond composite signal to a second auxiliary electrical signal.Examples of suitable light sensors include germanium photodiodes (PDs),and avalanche photodiodes (APDs).

The first light-combining component 111 combines the first portion ofthe comparative signal and the first portion of the reference signalinto a first composite signal. Due to the difference in frequenciesbetween the first portion of the comparative signal and the firstportion of the reference signal, the first composite signal is beatingbetween the first portion of the comparative signal and the firstportion of the reference signal. The light-combining component 111 alsosplits the first composite signal onto a first detector waveguide 121and a second detector waveguide 122.

The first detector waveguide 121 carries a first portion of the firstcomposite signal to a first light sensor 123 that converts the firstportion of the second composite signal to a first electrical signal. Thesecond detector waveguide 122 carries a second portion of the secondcomposite signal to a second auxiliary light sensor 124 that convertsthe second portion of the second composite signal to a second electricalsignal. Examples of suitable light sensors include germanium photodiodes(PDs), and avalanche photodiodes (APDs).

The first reference waveguide 110 and the second reference waveguide 108are constructed to provide a phase shift between the first portion ofthe reference signal and the second portion of the reference signal. Forinstance, the first reference waveguide 110 and the second referencewaveguide 108 can be constructed so as to provide a 90 degree phaseshift between the first portion of the reference signal and the secondportion of the reference signal. As an example, one reference signalportion can be an in-phase component and the other a quadraturecomponent. Accordingly, one of the reference signal portions can be asinusoidal function and the other reference signal portion can be acosine function. In one example, the first reference waveguide 110 andthe second reference waveguide 108 are constructed such that the firstreference signal portion is a cosine function and the second referencesignal portion is a sine function. Accordingly, the portion of thereference signal in the second composite signal is phase shiftedrelative to the portion of the reference signal in the first compositesignal, however, the portion of the comparative signal in the firstcomposite signal is not phase shifted relative to the portion of thecomparative signal in the second composite signal.

The first light sensor 123 and the second light sensor 124 can beconnected as a balanced detector and the first auxiliary light sensor118 and the second auxiliary light sensor 120 can also be connected as abalanced detector. For instance, FIG. 6B provides a schematic of therelationship between the electronics, the first light sensor 123, thesecond light sensor 124, the first auxiliary light sensor 118, and thesecond auxiliary light sensor 120. The symbol for a photodiode is usedto represent the first light sensor 123, the second light sensor 124,the first auxiliary light sensor 118, and the second auxiliary lightsensor 120 but one or more of these sensors can have otherconstructions. In some instances, all of the components illustrated inthe schematic of FIG. 6B are included on the LIDAR system. In someinstances, the components illustrated in the schematic of FIG. 6B aredistributed between the LIDAR system and electronics located off of theLIDAR system.

The electronics connect the first light sensor 123 and the second lightsensor 124 as a first balanced detector 125 and the first auxiliarylight sensor 118 and the second auxiliary light sensor 120 as a secondbalanced detector 126. In particular, the first light sensor 123 and thesecond light sensor 124 are connected in series. Additionally, the firstauxiliary light sensor 118 and the second auxiliary light sensor 120 areconnected in series. The serial connection in the first balanceddetector is in communication with a first data line 128 that carries theoutput from the first balanced detector as a first data signal. Theserial connection in the second balanced detector is in communicationwith a second data line 132 that carries the output from the firstbalanced detector as a second data signal. The first data signal and thesecond data signal are beating as a result of the beating between thecomparative signal and the reference signal, i.e. the beating in thefirst composite signal and in the second composite signal.

The first data line 128 carries the first data signal to a first switch134. The first switch can be in a first configuration where the firstdata signal is carried to a distance branch 136 or in a secondconfiguration where the first data signal is carried to a velocitybranch 138. In FIG. 6B, the first switch 134 is shown in the firstconfiguration. The second data line 132 carries the second data signalto a second switch 140. The second switch can be in a firstconfiguration where the second data signal is carried to the distancebranch 136 or in a second configuration where the second data signal iscarried to a velocity branch 138. In FIG. 6B, the second switch 140 isshown in the first configuration. A suitable switch for use as the firstswitch and/or second switch includes, but is not limited to, anelectromechanical switch, and a solid state MOSFET or PIN diode switch.

The electronics operate the first switch and the second switch such thatthey are in the same configuration during the first period and duringthe second period. For instance, the electronics can operate the firstswitch and the second switch such that the first switch and the secondswitch are both in the first configuration during the first period andboth in the second configuration during the second period. In thisexample, the first data signal and the second data signal are carried tothe distance branch 136 during the first period and to the velocitybranch 138 during the second period.

During operation of the LIDAR system, the generation of LIDAR data isdivided into a series of cycles where LIDAR data is generated for eachcycle. In some instances, each of the cycles corresponds to a differentsample region in the field of view. Accordingly, different cycles cangenerate LIDAR data for different regions in a field of view.

The cycles can be performed such that the time for each cycle can bedivided into different time periods that include a distance time period(first period) and a velocity time period (second period). The distancebetween the reflecting object and the LIDAR chip can be determined inthe distance period and the radial velocity between the reflectingobject and the LIDAR chip can be determined in the velocity period.

The electronics are configured to use the first data signal and thesecond data signal to determine or approximate at least the distancebetween the LIDAR system and the reflecting object. For instance, duringthe first period, the electronics can operate the modulator 14 so as toadd chirp to the amplitude of the outgoing light signal and accordinglythe LIDAR output signal. Adding chirp to the amplitude can includemodulating the amplitude of the outgoing light signal such that theamplitude of the outgoing light signal is a function of a sinusoid. Inone example, the amplitude of the outgoing light signal is modulatedsuch that the amplitude of the outgoing light signal is a square root ofa function that includes a sinusoid and/or is a square root of asinusoid. For instance, the outgoing light signal can be modulated so asto produce a modulated outgoing light signal and LIDAR output signalmathematically represented by Equation 1:(M+N*cos(C*t+D*t²)^(1/2)cos(F*t) where M, N, C, D and F are constants, trepresents time, M>0, N>0, and M≥N in order to prevent the radicand frombecoming negative, C>0, D≠0. As will become evident below, F can be afunction of the frequency of the LIDAR output signal (f_(c)). InEquation 1, F and C can be selected such that F>>C.

The distance branch includes a first distance branch line 142. Duringthe first period, the first distance branch line 142 carries the firstdata signal to a first multiplier 144. In FIG. 6B, the first multiplier144 is configured to square the amplitude of the first data signal andto output a first multiplied data signal. The distance branch includes asecond distance branch line 146. During the first period, the seconddistance branch line 146 carries the second data signal to a secondmultiplier 148. In FIG. 6B, the second multiplier 148 is configured tosquare the amplitude of the second data signal and to output a secondmultiplied data signal. Suitable first multipliers and/or secondmultipliers include, but are not limited to, RF mixers such as a Gilbertcell mixer.

The distance branch includes an adder 150 that sums the first multiplieddata signal and the second multiplied data signal. The adder outputs asummed data signal. Suitable adders include, but are not limited to, RFcombiners including resistive or hybrid combiners. The distance branchincludes a low-pass filter 152 that receives the summed data signal andoutputs a beating data signal. The low-pass filter is selected to removehigher frequency contributions to the summed data signal that areartifacts of the mixing of the reference and return signals. Thelow-pass filter can be selected to have a bandwidth greater than orequal to: f_(dmax)/2+ατ_(0max) where f_(dmax) represents the maximumlevel of the Doppler shift of the LIDAR input signal relative to theLIDAR input signal for which the LIDAR system is to provide reliableresults, τ_(0max) represents maximum delay between transmission of theLIDAR output signal and the receipt of the LIDAR input signal, and arepresents the rate of change in the frequency of the chirp added to theamplitude of the modulated outgoing light signal during the duration ofthe sample period (i.e. the first period). In some instances, a isdetermined from B/T where B represents the change in the frequency ofthe chirp added to the amplitude of the modulated outgoing light signalduring the duration of the sample period and T is the duration of thesample period. In some instances, T is determined from

$T = {\frac{\lambda_{c}}{2\; \Delta \; v_{\min}} + \tau_{0\max}}$

where λ_(c) represents the wavelength of the outgoing light signal,Δv_(min): represents velocity resolution and B can be determined from

$B = \frac{cT}{2\left( {T - \tau_{0\max}} \right)\Delta \; R_{\min}}$

where c represents the speed of light and

represents distance resolution. In some instances, the filter has abandwidth greater than 0.1 GHz, 0.2 GHz, or 0.3 GHz and/or less than 0.4GHz, 0.5 GHz, or 1 GHz. Corresponding values for the sweep period (T)can be 10 μs, 8 μs, 4 μs, 3 μs, 2 μs, and 1 μs.

The distance branch includes an Analog-to-Digital Converter (ADC) 154that receives the beating data signal from the filter. TheAnalog-to-Digital Converter (ADC) 154 converts the beating data signalfrom an analog form to digital form and outputs the result as a digitalLIDAR data signal. As discussed above, the conversion of the beatingdata signal includes sampling the beating data signal at a samplingrate. The addition of the chirp to the amplitude of the LIDAR outputsignal substantially reduces or removes the effects of radial velocityfrom the beating of the composite signal and the resulting electricalsignals. For instance, the frequency shift of the LIDAR output signalrelative to the LIDAR input signal (“frequency shift,” Δf) can bewritten as Δf=Δf_(d)+Δf_(s) where Δf_(d) represents the change infrequency due to the Doppler shift and Δf_(s) is the change in frequencydue to the separation between the reflecting object and the LIDARsystem. The outgoing light signal can be modulated so as to produce amodulated outgoing light signal and accordingly, a LIDAR output signalthat is also modulated, where the change in frequency due to the Dopplershift (Δf_(d)) is less than 10%, 5%, 1%, or even 0.1% of the Dopplershift that would occur from a sinusoidal LIDAR output signal serving asthe LIDAR and having a constant amplitude and the same frequency as themodulated outgoing light signal and/or the LIDAR output signal. Forinstance, the outgoing light signal and/or the LIDAR output signal canbe modulated so as to produce a modulated outgoing light signal and/or aLIDAR output signal where the change in frequency due to the Dopplershift (Δf_(d)) is less than 10%, 5%, 1%, or even 0.1% of the Dopplershift that would occur from a continuous wave serving as the LIDARoutput signal and having the same frequency as the modulated outgoinglight signal and/or the LIDAR output signal. In another example, theoutgoing light signal and/or the LIDAR output signal are modulated so asto produce a modulated outgoing light signal and/or a LIDAR outputsignal where the change in frequency due to the Doppler shift (Δf_(d))is less than 10%, 5%, 1%, or even 0.1% of the Doppler shift that wouldoccur from the outgoing light signal before modulation (the unmodulatedoutgoing light signal) serving as the LIDAR output signal. These resultscan be achieved by increasing the value of the Equation 1 variable Frelative to C. For instance, F can represent 2πf_(c) and C can represent2πf₁ where f₁ denotes the base frequency of the frequency-chirp in theamplitude of the modulated outgoing light signal. Accordingly, F can beincreased relative to C by increasing the value of the frequency of theLIDAR output signal (f_(c)) relative to the chirp base frequency (f₁).As an example, f_(c) and f₁ can be selected such that f_(c)>>f₁. In someinstances, f_(c) and f₁ are selected such that a ratio of f_(c):f₁ isgreater than 2:1, 10:1, 1×10⁴:1, 5×10⁴, or 1×10⁵:1 and/or less than5×10⁵, 1×10⁶, 5×10⁶ or 5×10⁸. Accordingly, the variables F and C canalso have these same values for a ratio of F:C. The reduction and/orremoval of the change in frequency due to the Doppler shift (Δf_(d))from the frequency shift lowers the beat frequency and accordinglyreduces the required sampling rate.

The distance branch includes a transform module 156 that receives thedigital LIDAR data signal from the Analog-to-Digital Converter (ADC)154. The transform module 156 is configured to perform a real transformon the digital LIDAR data signal so as to convert from the time domainto the frequency domain. This conversion provides an unambiguoussolution for the shift in frequency of the shift of the LIDAR inputsignal relative to the LIDAR input signal that is caused by the distancebetween the reflecting object and the LIDAR system. A suitable realtransform is a Fourier transform such as a Fast Fourier Transform (FFT).The classification of the transform as a real transform distinguishesthe transform from complex transforms such as complex Fouriertransforms. The transform module can execute the attributed functionsusing firmware, hardware or software or a combination thereof.

Since the frequency provided by the transform module does not have inputfrom, or does not have substantial input from, a frequency shift due torelative movement, the determined frequency shift can be used toapproximate the distance between the reflecting object and the LIDARsystem. For instance, the electronics can approximate the distancebetween the reflecting object and the LIDAR system (R₀) using Equation3: R₀=c*Δf/(2α) where Δf can be approximated as the peak frequencyoutput from the transform module, and c is the speed of light.

The velocity branch can be configured to use the first data signal andthe second data signal to determine or approximate at least the radialvelocity of the LIDAR system and the reflecting object. The LIDAR outputsignal with a frequency that is a function of time disclosed in thecontext of FIG. 1 through FIG. 2 can be replaced by a LIDAR outputsignal where the frequency of the LIDAR output signal is not a functionof time. For instance, the LIDAR output signal can be a continuous wave(CW). For instance, during the second period, the modulated outgoinglight signal, and accordingly the LIDAR output signal, can be anunchirped continuous wave (CW). As an example the modulated outgoinglight signal, and accordingly the LIDAR output signal, can berepresented by Equation 2: G*cos(H*t) where G and H are constants and trepresents time. In some instances, G represents the square root of thepower of the outgoing light signal and/or H represents the constant Ffrom Equation 1. In instances where the output of the light source hasthe waveform that is desired for the modulated outgoing light signal,the electronics need not operate the modulator 14 so as to modify theoutgoing light signal. In these instances, the output of the lightsource(s) can serve as the modulated outgoing light signal andaccordingly the LIDAR output signal. In some instances, the electronicsoperate the modulator 14 so as to generate a modulated outgoing lightsignal with the desired form.

Since the frequency of the LIDAR output signal is constant in the secondperiod, changing the distance between reflecting object and LIDAR systemdoes not cause a change to the frequency of the LIDAR input signal. As aresult, the separation distance does not contribute to the shift in thefrequency of the LIDAR input signal relative to the frequency of theLIDAR output signal. Accordingly, the effect of the separation distancehas been removed or substantially from the shift in the frequency of theLIDAR input signal relative to the frequency of the LIDAR output signal.

The velocity branch includes a first velocity branch line 160 and asecond velocity branch line 160. During the second period, the firstvelocity branch line 160 carries the first data signal to anAnalog-to-Digital Converter (ADC) 164 which converts the first datasignal from an analog form to a digital form and outputs a first digitaldata signal. As discussed above, the conversion of the first data signalis done by sampling the first data signal at a sampling rate. The use ofa continuous wave as the LIDAR output signal substantially removes theeffects of distance between the reflecting object and LIDAR system fromthe beating of the composite signal and the resulting electricalsignals. Accordingly, the beating frequency is reduced and the requiredsampling rate is reduced.

The second velocity branch line 162 carries the second data signal to anAnalog-to-Digital Converter (ADC) 166 which converts the second datasignal from an analog form to a digital form and outputs a seconddigital data signal. As discussed above, the conversion of the seconddata signal includes sampling the second data signal at a sampling rate.The use of a continuous wave as the LIDAR output signal substantiallyreduces or removes the effects of distance between the reflecting objectand LIDAR system from the beating of the second composite signal and theresulting electrical signals. Accordingly, the beating frequency isreduced and the required sampling rate is reduced.

The sampling rate for the Analog-to-Digital Converter (ADC) 164 can bethe same or different from the sampling rate for the Analog-to-DigitalConverter (ADC) 166.

The velocity branch includes a transform module 168 that receives thefirst digital data signal from the Analog-to-Digital Converters (ADC)164 and the second digital data signal from the Analog-to-DigitalConverters (ADC) 166. Since the first data signal is an in-phasecomponent and the second data signal its quadrature component, the firstdata signal and the second data signal together act as a complexvelocity data signal where the first data signal is the real componentand the second data signal is the imaginary component. As a result, thefirst digital data signal can be the real component of a digitalvelocity data signal and the second data signal can be the imaginarycomponent of the digital velocity data signal. The transform module 168can be configured to perform a complex transform on the digital velocitydata signal so as to convert from the time domain to the frequencydomain. This conversion provides an unambiguous solution for the shiftin frequency of LIDAR input signal relative to the LIDAR input signalthat is caused by the radial velocity between the reflecting object andthe LIDAR system. A suitable complex transform is a Fourier transformsuch as a complex Fast Fourier Transform (FFT). The transform module canexecute the attributed functions using firmware, hardware or software ora combination thereof.

Since the frequency shift provided by the transform module 168 does nothave input from a frequency shift due to the separation distance betweenthe reflecting object and the LIDAR system, and because of the complexnature of the velocity data signal, the output of the transform module168 can be used to approximate the radial velocity between thereflecting object and the LIDAR system. For instance, the electronicscan approximate the radial velocity between the reflecting object andthe LIDAR system (v) using Equation 4: v=c*f_(d)/(2*f_(c)) where f_(d)is approximated as the peak frequency output from the transform module168, c is the speed of light, and f_(c) represents the frequency of theLIDAR output signal.

Additional components can be added to the schematic of FIG. 6B. Forinstance, when the LIDAR system generates multiple LIDAR output signalsor is used with other LIDAR systems that generate LIDAR output signals(i.e., by means of frequency or wavelength division multiplexing,FDM/WMD), the LIDAR system can include one or more filters to removeinterfering signals from the real and/or imaginary components of thebeating data signal and/or of the velocity data signal. Accordingly, theLIDAR system can include one or more filters in addition to theillustrated components. Suitable filters include, but are not limitedto, lowpass filters. In the case of the optical design, if the frequencyof the interfering components fall outside the bandwidth of the balancedetector(s), additional filtering may not be necessary as it may beeffectively provided by the balance detector(s).

The sampling rate that is used during the first period and the secondperiod can be selected to have a value that is greater than or equal tothe larger of two values selected from the group consisting of theminimum sampling rate for the first period and the minimum sampling ratefor the second period. For instance, during the first period the rangeof rates for the first period sampling rate (f_(s1)) can be determinedby

where τ_(0max) represents the maximum amount of time between thetransmission of the LIDAR output signal and the receipt of the LIDARinput signal. During the second period the range of rates for the secondperiod sampling rate (f_(s2)) can be determined by

where f_(dmax) represents the maximum level of the Doppler shift of theLIDAR input signal relative to the LIDAR input signal for which theLIDAR system is to provide reliable results. The maximum is determinedby the largest level for which the LIDAR system is to provide reliableresults. Accordingly, the maximum distance generally corresponds to thedistance for the field of view set in the LIDAR specifications and themaximum Doppler shift generally corresponds to the Doppler shift thatwould occur at the maximum radial velocity values set in thespecifications. These two equations show that the minimum sampling ratefor the first period is 2ατ_(0max) and the minimum sampling rate for thesecond period is 2f_(dmax). As a result, the sampling rate is selectedto have a value that is greater than or equal to the larger of2ατ_(0max) and 2f_(dmax). In other words, the sample rate used duringthe first period and the second period (f_(s)) is f_(s)≥max(2ατ_(0max),2f_(dmax)). In some instances, the sample rate used during the firstperiod and the second period (f_(s)) is greater than or equal to 0.1GHz, 0.2 GHz, or 0.5 GHz and/or less than 1 GHz, 2 GHz, or 4 GHZ.

FIG. 6C provides another example of a schematic of electronics that aresuitable for extracting LIDAR data with a processing unit constructedaccording to FIG. 7A. The electronics connect the first light sensor 123and the second light sensor 124 as a first balanced detector 125 and thefirst auxiliary light sensor 118 and the second auxiliary light sensor120 as a second balanced detector 126. In particular, the first lightsensor 123 and the second light sensor 124 are connected in series.Additionally, the first auxiliary light sensor 118 and the secondauxiliary light sensor 120 are connected in series. The serialconnection in the first balanced detector is in communication with afirst data line 128 that carries the output from the first balanceddetector as a first data signal. The serial connection in the secondbalanced detector is in communication with a second data line 132 thatcarries the output from the second balanced detector as a second datasignal. The first data signal is an electrical representation of thefirst composite signal and the second data signal is an electricalrepresentation of the second composite signal. Accordingly, the firstdata signal includes a contribution from a first waveform and a secondwaveform and the second data signal is a composite of the first waveformand the second waveform. The portion of the first waveform in the firstdata signal is phase-shifted relative to the portion of the firstwaveform in the first data signal but the portion of the second waveformin the first data signal being in-phase relative to the portion of thesecond waveform in the first data signal. For instance, the second datasignal includes a portion of the reference signal that is phase shiftedrelative to a different portion of the reference signal that is includedthe first data signal. Additionally, the second data signal includes aportion of the comparative signal that is in-phase with a differentportion of the comparative signal that is included in the first datasignal. The first data signal and the second data signal are beating asa result of the beating between the comparative signal and the referencesignal, i.e. the beating in the first composite signal and in the secondcomposite signal.

The electronics 62 include a transform mechanism 138 configured toperform a mathematical transform on the first data signal and the seconddata signal. For instance, the mathematical transform can be a complexFourier transform with the first data signal and the second data signalas inputs. Since the first data signal is an in-phase component and thesecond data signal its quadrature component, the first data signal andthe second data signal together act as a complex data signal where thefirst data signal is the real component and the second data signal isthe imaginary component of the input.

The transform mechanism 138 includes a first Analog-to-Digital Converter(ADC) 164 that receives the first data signal from the first data line128. The first Analog-to-Digital Converter (ADC) 164 converts the firstdata signal from an analog form to a digital form and outputs a firstdigital data signal. The transform mechanism 138 includes a secondAnalog-to-Digital Converter (ADC) 166 that receives the second datasignal from the second data line 132. The second Analog-to-DigitalConverter (ADC) 166 converts the second data signal from an analog formto a digital form and outputs a second digital data signal. The firstdigital data signal is a digital representation of the first data signaland the second digital data signal is a digital representation of thesecond data signal. Accordingly, the first digital data signal and thesecond digital data signal act together as a complex signal where thefirst digital data signal acts as the real component of the complexsignal and the second digital data signal acts as the imaginarycomponent of the complex data signal.

The transform mechanism 138 includes a transform component 168 thatreceives the complex data signal. For instance, the transform component168 receives the first digital data signal from the firstAnalog-to-Digital Converter (ADC) 164 as an input and also receives thesecond digital data signal from the first Analog-to-Digital Converter(ADC) 166 as an input. The transform component 168 can be configured toperform a mathematical transform on the complex signal so as to convertfrom the time domain to the frequency domain. The mathematical transformcan be a complex transform such as a complex Fast Fourier Transform(FFT). A complex transform such as a complex Fast Fourier Transform(FFT) provides an unambiguous solution for the shift in frequency ofLIDAR input signal relative to the LIDAR output signal that is caused bythe radial velocity between the reflecting object and the LIDAR chip.The transform component 168 can execute the attributed functions usingfirmware, hardware or software or a combination thereof.

The Complex Fourier transform converts the input from the time domain tothe frequency domain, the Complex Fourier transform outputs a singlefrequency peak for each object located in the sample region. Thefrequency associated with this peak is used by the electronics as theshift in frequency of LIDAR input signal relative to the LIDAR outputsignal is caused by the radial velocity between the reflecting objectand the LIDAR chip and/or the distance between the reflecting object andthe LIDAR chip. Prior methods of resolving the frequency of the LIDARinput signal made use of real Fourier transforms rather than the ComplexFourier transform technique disclosed above. These prior methods outputmultiple frequency peaks for each object in a sample region.Accordingly, the prior methods output multiple different frequenciesthat are both associated with each object in the sample region in thateach of the associated frequencies would not be present if the objectwere removed from the sample region. As noted above, when using LIDARapplications, it can become difficult to identify the correct peak.Since the above technique for resolving the frequency generates a singlesolution for the frequency, the ambiguity with the frequency solutionhas been resolved.

The electronics can use each frequency peak output from the transform togenerate LIDAR data. For instance, the electronics can operate the lightsource such that the LIDAR output signal alternates periods with anincreasing frequency and periods with a decreasing frequency as shown inFIG. 2C. The following equation applies during a data period where theelectronics increase the frequency of the LIDAR output during the dataperiod such as occurs with the LIDAR output signal 2C during the firstperiod:

where f_(ub) is the frequency provided by the transform component, f_(d)represents the Doppler shift

(f_(d) = 2vf_(c)/c)

where f_(c) is the frequency of the LIDAR output signal at the start ofthe data period (i.e. t=0), v is the radial velocity between thereflecting object and the LIDAR chip where the direction from thereflecting object toward the chip is assumed to be the positivedirection, and c is the speed of light, α represents the rate at whichthe frequency of the outgoing light signal is increased or decreasedduring the period, and τ₀ is the roundtrip delay (time between the LIDARoutput signal exiting from the LIDAR chip and the associated LIDAR inputsignal returning to the LIDAR chip) for a stationary reflecting object.The following equation applies during a data period where electronicsdecrease the frequency of the LIDAR output signal during the period suchas occurs with the LIDAR output signal of FIG. 2C during the secondperiod:

−f_(db) = −f_(d) − ατ₀

where f_(db) is the frequency provided by the transform mechanism. Inthese two equations, f_(d) and τ₀ are unknowns. These two equations aresolved for the two unknowns f_(d) and τ₀. The values of f_(db) andf_(ub) that are substituted into the solution come from the same channeland accordingly the same processing units (labeled 34 in FIG. 1), butduring different data periods in the same cycle. Since the cycles isassociated with a sample region in the field of view, the solutionyields the values of f_(d) and τ₀ for a sample region in the field ofview. The radial velocity for that sample region can then be determinedfrom the Doppler shift (v=c*f_(d)/(2f_(c))) and the separation distancefor that sample region can be determined from c*τ₀/2. As a result, theLIDAR data for a sample regions is determined for a single LIDAR outputsignal (channel) that illuminates the sample region.

As discussed above, the LIDAR system can output more than two LIDARoutput signals that each carries a different channel. For instance, theLIDAR system can output multiple LIDAR output signals that havefrequency versus time waveforms according to FIG. 2C. The LIDAR outputsignals can be concurrently directed to the same sample region in afield of view or different portions of the LIDAR output signals can bedirected to different sample regions in the field of view. Additionally,the LIDAR output signals can be sequentially scanned across the sampleregions such that each sample region is illuminated by at least one ofthe LIDAR output signals.

The above descriptions of the LIDAR system operation assumes that amodulator is present on the utility waveguide 12; however, in someinstances, the modulator is optional. In these instances, theelectronics can operate the light source(s) 10 so as to tune thefrequency of the LIDAR output signal as desired. Since one or more ofthe light sources can output multiple channels, tuning the frequency ofone light sources can concurrently tune the frequency of multiplechannels and accordingly multiple LIDAR output signals. For instance,tuning the frequency of a comb laser concurrently tunes the frequency ofthe channels output from that comb laser and accordingly tunes the LIDARoutput signals that carry the channels output from that comb laser. Theelectronics can tune the frequency of a light source such as a comblaser by tuning the electrical current driven through the comb laser. Insome instances, the electronics can tune the frequency of a light sourcesuch as a comb laser by 10 GHz, 100 GHz, and 1 THz.

The above descriptions of the LIDAR system operation assumes that amodulator is present on the utility waveguide 12; however, the modulatoris optional. In these instances, the electronics can operate the lightsource(s) 10 so as to increase the frequency of the outgoing lightsignal during the first period and during the second period theelectronics can decrease the frequency of the outgoing light signal asshown in FIG. 2C. Other examples of methods for extracting the LIDARdata from the resulting composite signals are disclosed in U.S. PatentApplication Ser. No. 62/671,913, filed on May 15, 218, entitled “OpticalSensor Chip,” and incorporated herein in its entirety.

FIG. 7 illustrates an example of a suitable optical port 26 thatincludes demultiplexing functionality and beam steering capability. Theoptical port 26 includes a splitter 184 that receives the outgoing lightsignal from the LIDAR signal waveguide 24. The splitter divides theoutgoing light signal into multiple output signals that are each carriedon a steering waveguide 186. Each of the steering waveguides ends at afacet 188. The facets are arranged such that the output signals exitingthe chip through the facets combine to form the LIDAR output signal.

The splitter and steering waveguides can be constructed such that thereis not a phase differential between output signals at the facet ofadjacent steering waveguides. For instance, the splitter can beconstructed such that each of the output signals is in-phase uponexiting from the splitter and the steering waveguides can each have thesame length. Alternately, the splitter and steering waveguides can beconstructed such that there is a linearly increasing phase differentialbetween output signals at the facet of adjacent steering waveguides. Forinstance, the steering waveguides can be constructed such that the phaseof steering waveguide number j is f_(o)+(j−1)f where j is an integerfrom 1 to N and represents the number associated with a steeringwaveguide when the steering waveguides are sequentially numbered asshown in FIG. 5, f is the phase differential between neighboringsteering waveguides when the phase tuners (discussed below) do notaffect the phase differential, and f_(o) is the phase of the outputsignal at the facet of steering waveguide k=1. Because the channels canhave different wavelengths, the values of f and f_(o) can each beassociated with one of the channels. In some instances, this phasedifferential is achieved by constructing the steering waveguides suchthat the steering waveguides have a linearly increasing lengthdifferential. For instance, the length of steering waveguide j can berepresented by l_(o)+(k−1)Δl where k is an integer from 1 to K andrepresents the number associated with a steering waveguide when thesteering waveguides are sequentially numbered as shown in FIG. 7, Δl isthe length differential between neighboring steering waveguide, andL_(o) is the length of steering waveguide k=1. Because Δl is a differentpercent of the wavelength of different channels included in the outputsignals, each of the different LIDAR output signals travels away fromLIDAR chip in a different direction (θ). When the steering waveguidesare the same length, the value of Δl is zero and the value of f is zero.Suitable Δl include, but are not limited to, Δl greater than 0, or 5and/or less than 10, or 15 μm. Suitable f include, but are not limitedto, f greater than 0π, or 7π and/or less than 15π, or 20π. Suitable Ninclude, but are not limited to, N greater than 10, or 500 and/or lessthan 1000, or 2000. Suitable splitters include, but are not limited to,star couplers, cascaded Y-junctions and cascaded 1X2 MMI couplers.

A phase tuner 190 can be positioned along at least a portion of thesteering waveguides. Although a phase tuner is shown positioned alongthe first and last steering waveguide, these phase tuners are optional.For instance, the chip need not include a phase tuner on steeringwaveguide j=1.

The electronics can be configured to operate the phase tuners so as tocreate a phase differential between the output signals at the facet ofadjacent steering waveguides. The electronics can operate the phasetuners such that the phase differential is constant in that it increaseslinearly across the steering waveguides. For instance, electronics canoperate the phase tuners such that the tuner-induced phase of steeringwaveguide number k is (k−1)α where k is an integer from 1 to N andrepresents the number associated with a steering waveguide when thesteering waveguides are sequentially numbered as shown in FIG. 7, a isthe tuner-induced phase differential between neighboring steeringwaveguides. Accordingly, the phase of steering waveguide number k isf_(o)+(k−1)f+(k−1)α. FIG. 5 illustrates the chip having only 4 steeringwaveguides in order to simplify the illustration, however, the chip caninclude more steering waveguides. For instance, the chip can includemore than 4 steering waveguides, more than 100 steering waveguides, ormore than 1000 steering waveguides and/or less than 10000 steeringwaveguides.

The electronics can be configured to operate the phase tuners so as totune the value of the phase differential α. Tuning the value of thephase differential α changes the direction that the LIDAR output signaltravels away from the chip (θ). Accordingly, the electronics can scanthe LIDAR output signal by changing the phase differential α. The rangeof angles over which the LIDAR output signal can be scanned is ϕ_(R)and, in some instances, extends from ϕ_(v) to −ϕ_(v) with ϕ=0° beingmeasured in the direction of the LIDAR output signal when α=0. When thevalue of Δl is not zero, the length differential causes diffraction suchthat light of different wavelengths travels away from chip in differentdirections (θ). Accordingly, there may be some spreading of the outgoinglight signal as it travels away from the chip. Further, changing thelevel of diffraction changes the angle at which the outgoing lightsignal travels away from the chip when α=0°. However, providing thesteering waveguides with a length differential (Δl≠0) can simplify thelayout of the steering waveguides on the chip.

Additional details about the construction and operation of an opticalport 26 constructed according to FIG. 7 can be found in U.S. ProvisionalPatent Application Ser. No. 62/680,787, filed on Jun. 5, 2018, andincorporated herein in its entirety.

The above LIDAR systems can be integrated on a single chip. A variety ofplatforms can be employed for a chip that includes the above LIDARsystems. A suitable platform includes, but is not limited to, asilicon-on-insulator wafer. One or more of the above components and/orportions of the above components can be integral with the chip or can beplaced on the chip with technologies such as flip-chip bondingtechnologies. For instance, a light source 10 can include a gain elementand one or more other components such as waveguides. The waveguide canbe integral with the chip and the gain element can be a component thatis separate from the chip but attached to the chip with a flip-chipbonding. Alternately, the above LIDAR system can be constructed withdiscrete components. For instance, all or a portion of the waveguidescan be optical fibers connecting discrete components, including a fiberoptical switch. Alternately, one or more portions of the LIDAR systemcan be integrated on a chip while other portions are discretecomponents. For instance, the utility waveguide 12 can be or include anoptical fiber that provides optical communication between a light source10 and an optical chip that includes the remainder of the LIDAR system.

A variety of optical switches that are suitable for use with the LIDARsystem can be constructed on planar device optical platforms such assilicon-on-insulator platforms. Examples of suitable optical switchesfor integration into the silicon-on-insulator platform include, but arenot limited to, Mach-Zehnder interferometers. FIG. 8 is a schematic of aMach-Zehnder interferometer. The switch includes a first switchwaveguide 200 that connects the comparative signal waveguide 28 and thereference signal waveguide 36. A second switch waveguide 202 connectsthe utility waveguide 12 and the LIDAR signal waveguide 24. The firstswitch waveguide 200 and the second switch waveguide 202 are included ina first optical coupler 204 and in a second optical coupler 206. A phaseshifter 208 is positioned along the first switch waveguide 200 or thesecond switch waveguide 200 between the first optical coupler 204 andthe second optical coupler 206. Suitable phase shifters include, but arenot limited to, PIN diodes, PN junctions operated in carrier depletionmode, and thermal heaters. The electronics can operate the phase shifterso as to change the switch between the pass mode and the switched mode.

The optical switches are disclosed above as being configured such thatthe outgoing light signal is directed to the LIDAR signal waveguide 24and an incoming light signal would be directed to the utility waveguide12 in the pass mode and such that the outgoing light signal is directedto the reference signal waveguide 36 and the incoming light signal isdirected to the comparative signal waveguide 28 in the switched mode.However, the waveguides can optionally be arranged such that theoutgoing light signal is directed to the LIDAR signal waveguide 24 andan incoming light signal would be directed to the utility waveguide 12in the switched mode and such that the outgoing light signal is directedto the reference signal waveguide 36 and the incoming light signal isdirected to the comparative signal waveguide 28 in the pass mode. Inthese instances, the LIDAR system can be operated as disclosed above butwith the switched mode and pass mode switched so as to achieve the sameresults described above. As a result, the terms pass mode and switchedmode need to refer to specific operational mode but instead to differentmodes of switch operation such as a first mode and a second mode.

Other embodiments, combinations and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. Therefore, this invention is to be limited only by thefollowing claims, which include all such embodiments and modificationswhen viewed in conjunction with the above specification and accompanyingdrawings.

1. A LIDAR system, comprising: a common optical pathway through a LIDARsystem that is traveled by an outgoing light signal that exits the LIDARsystem and also by an incoming light signal that enters the LIDAR systemafter being reflected by an object and that includes light from theoutgoing light signal; an optical switch positioned along the commonoptical pathway and configured to be operated in different modes, theincoming light signal and/or the outgoing light signal being routedalong a different optical path through the LIDAR system in response tothe optical switch being in a different mode.
 2. The LIDAR system ofclaim 1, further comprising: electronics configured to switch theoptical switch between the different modes.
 3. The LIDAR system of claim1, wherein the outgoing light signal exits from the LIDAR system whenthe optical switch is in a first one of the modes but does not exit fromthe LIDAR system when the optical switch is in a second one of themodes.
 4. The LIDAR system of claim 3, wherein light from the outgoinglight is mixed with light from the incoming light signal so as togenerate a composite light signal when the optical switch is in thesecond mode.
 5. The LIDAR system of claim 4, wherein the composite lightsignal is not generated when the optical switch is in the first mode. 6.The LIDAR system of claim 4, wherein the incoming light signal and theoutgoing light signal both travel along the common optical path when theoptical switch is in the first mode.
 7. The LIDAR system of claim 4,wherein the incoming light signal travels along the common optical pathwhen the optical switch is in the second mode but the outgoing lightsignal does not travel along the common optical path when the opticalswitch is in the second mode.
 8. The LIDAR system of claim 4, whereinthe incoming light signal travels away from the optical switch along afirst optical path when the optical switch is in the second mode, theoutgoing light signal travels away from the optical switch along asecond optical path when the optical switch is in the second mode, thefirst optical path being separate from the second optical path, and thecommon optical path being separate from the first optical path beingseparate from the second optical path.
 9. The LIDAR system of claim 1,wherein the outgoing light signal travels away from the optical switchalong the common optical pathway and the incoming light signal travelstoward the optical switch along the common optical pathway.
 10. TheLIDAR system of claim 1, wherein the optical switch is a cross-overswitch.
 11. The LIDAR system of claim 1, further comprising: electronicsthat switch the optical switch between the different modes, thedifferent modes including a first mode and a second mode, theelectronics operating the switch through a series or periods that eachincludes a transmit segment and a receiver period, the electronicsoperating the switch in the first mode during the transmit segment andin the second mode during the receive segment.
 12. The LIDAR system ofclaim 11, wherein the electronics tune a duration of the transmitsegment and/or the receive segment.
 13. The LIDAR system of claim 12,wherein the duration of the transmit segment and/or the receive segmentis tuned in response to a change in a distance between the LIDAR systemand an object that is located remotely from the LIDAR system butreflects the outgoing light signal after the outgoing light signal exitsfrom the LIDAR system.
 14. The LIDAR system of claim 12, wherein theduration of the transmit segment and/or the receive segment is tuned inresponse to a change in a distance between the LIDAR system and a fieldof view associated with the LIDAR system.
 15. The LIDAR system of claim12, wherein the duration of the transmit segment (t_(ts)) and/or thereceive segment (t_(rs)) is tuned such that a value of(t_(rs)/(t_(rs)+t_(rs))) is less than D′/(1+D′) where D′=D/D_(max) whereD represents a distance between the LIDAR system and an object that islocated remotely from the LIDAR system or a distance between the LIDARsystem and a field of view and D_(max) represents a maximum value for Dfor which the LIDAR system is configured to generate LIDAR data.
 16. ALIDAR system, comprising: a light source configured to generate anoutgoing light signal that exits from the LIDAR system, the LIDAR systemconfigured to receive an incoming light signal that enters the LIDARsystem from outside of the LIDAR system and that includes light from theoutgoing light signal; an optical switch that receives the outgoinglight signal and the incoming light signal and configured to be operatedin different modes, the incoming light signal and/or the outgoing lightsignal being routed along a different optical path through the LIDARsystem in response to the optical switch being in a different mode. 17.The LIDAR system of claim 16, wherein the outgoing light signal exitsfrom the LIDAR system when the optical switch is in a first one of themodes but does not exit from the LIDAR system when the optical switch isin a second one of the modes.
 18. The LIDAR system of claim 17, whereinlight from the outgoing light is mixed with light from the incominglight signal so as to generate a composite light signal when the opticalswitch is in the second mode.
 19. The LIDAR system of claim 18, whereinthe composite light signal is not generated when the optical switch isin the first mode.